mathematical physicist working on quantum gravity using the techniques of higher-dimensional algebra

Here is my reply to your fiendish question:

How can we possibly pick the most important invention in the past two thousand years? The real biggies — language, fire, agriculture, art — came too soon. In the last two millennia our world has seen so many inventions that it's hard to think of one that stands above all the rest. The printing press? The computer? The A-bomb? After a bit of this, one is tempted to give a smart-aleck reply and back it up with the semblance of earnest reasoning: "Thousand Island dressing!"

But even this is boring. Somehow we have to break out of the box! Well, if inventions are important, surely it's even more important to invent the social structures that will guarantee a steady flow of new inventions. I've heard it said that Edison was the first to turn invention into a business. Every day he would walk into his lab and say "Okay, what can we invent today?" But the groundwork was laid earlier. Perhaps the invention of a patent office was the key step? Or further back, Bacon's "New Atlantis", which envisioned the techno-paradise we are now all so busy trying to build?